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Chemistry > Ch4.1 Basic Organic Concepts and Hydrocarbons > Flashcards

Ch4.1 Basic Organic Concepts and Hydrocarbons Flashcards

1
Q

What is a molecular formula?

A

Where the exact number of each atom in a molecule is shown

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2
Q

What is an empirical formula?

A

The simplest whole number ratio of atoms in a molecule

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3
Q

What is a structural formula?

A

Using conventional groups for minimal detail about unambiguous structure

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4
Q

What is a displayed formula?

A

Where the molecule is drawn with lines for bonds

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5
Q

What is a skeletal formula?

A

Shows a simplified organic formula by removing hydrogen atoms from alkyl chains to leave just carbon skeleton

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6
Q

What is a general formula?

A

Represents any member of a homologous series eg. alkanes or alkenes

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7
Q

What is the general formula for alcohols?

A

CnH2n+1OH

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8
Q

What is the general formula for an alkyl group?

A

CnH2n+1

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9
Q

What is an aliphatic hydrocarbon?

A

A compound containing carbon and hydrogen joined in straight chains, branched chains or non-aromatic rings

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10
Q

What is an alicyclic hydrocarbon?

A

An aliphatic compound arranged in non-aromatic rings with or without side chains

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11
Q

What is an aromatic hydrocarbon?

A

A compound containing a benzene ring

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12
Q

What does it mean if a hydrocarbon is saturated?

A

Contains single carbon-carbon bonds only

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13
Q

What does it mean if a hydrocarbon is unsaturated?

A

There is multiple double or triple carbon-carbon bonds or aromatic rings

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14
Q

What is a structural isomer?

A

Different name and structure, same molecular formula

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15
Q

What is a steroisomer?

A

Same chemical formula but a different arrangement of atoms in space

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16
Q

Define structural isomers

A

Isomers that have the same molecular formula but different structural formulae

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17
Q

What are the 2 types of covalent bond?

A

Sigma and Pi

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18
Q

Describe sigma bonds

A

The overlap of orbitals where the electrons in the overlap are located between the nuclei of the overlapping atoms

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19
Q

Describe Pi bonds

A

The overlap of orbitals where the electrons in the overlap are located above and below the nuclei of the overlapping atoms

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20
Q

Which is stronger out of a pi bond and a sigma bond?

A

Sigma bonds are stronger, in a reaction the Pi bonds will break first

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21
Q

How do Pi and Sigma bonds relate to single, double and triple covalent bonds?

A

single = 1 sigma
double = 1 sigma and 1 pi
triple = 1 sigma and 2 pi

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22
Q

How do boiling points differ between isomers?

A
  • higher in straight chains than branched
  • more branches = lower BP
  • branches decrease effectiveness of intermolecular forces
  • BP differs with different functional groups
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23
Q

Define stereoisomerism

A

Isomers that have the same structural formula but different arrangement of atoms in space

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24
Q

State 2 features of stereoisomers

A
  • come in pairs
  • the 2 isomers in the pair have the same name
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25
Q

Where is E/Z isomerism found?

A

In alkenes due to the restricted rotation caused by the C=C bonds

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26
Q

What is the condition needed for E/Z isomerism to occur?

A

Must be different atoms or groups attached to each side of the carbon atoms

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27
Q

What do the E and Z stand for in E/Z isomerism?

A

Entegen and Zusammen
Opposite and Together in German

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28
Q

What are the conditions for an E isomer?

A
  • the highest priority atoms are across the double bond
  • there isn’t an H alone on both C atoms in double bond
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29
Q

What are the conditions for a Z isomer?

A
  • the highest priority atoms are on the same side of the double bond
  • there isn’t an H alone on both C atoms in double bond
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30
Q

What are the conditions for a cis isomer?

A
  • the highest priority atoms are on the same side of the double bond
  • there is an H alone on both C atoms in double bond
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31
Q

What are the conditions for a trans isomer?

A
  • the highest priority atoms are across the double bond
  • there is an H alone on both C atoms in double bond
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32
Q

How is priority determined when deciding what kind of isomer a molecule is?

A

The higher the atomic number of the group attached to the Cs in the double bond, the higher the priority

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33
Q

What are the products of complete combustion?

A

Carbon dioxide and water

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34
Q

What are the products of incomplete combustion?

A

Carbon, carbon monoxide and water

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35
Q

What is heterolytic fission?

A

Unequal splitting of a covalent bond whereby ions are produced (pair of electrons tend to more electronegative element)

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36
Q

What is homolytic fission?

A

Equal splitting of a covalent bond whereby radicals are produced

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37
Q

What are radicals?

A
  • species with one or more unpaired electrons
  • formed by homolytic fission of covalent bonds
  • formed during reaction between chlorine and methane
  • formed during thermal cracking
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38
Q

What is the mechanism that is used in the chlorination of methane called?

A

Free radical substitution

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39
Q

What are the 3 steps called that are involved in free radical substitution for chlorination of methane and what happens to radicals during these steps?

A
  • initiation: radicals created
  • propagation: radicals used and regenerated
  • termination: radicals removed
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40
Q

What is covalent bond fission?

A

When in the first stage of a chemical reaction, activation energy affects the covalent bonds by causing them to break

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41
Q

What is homolytic fission?

A

Occurs when a covalent bond breaks and each electron goes to a different bonded atom. Generates 2 radicals

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42
Q

What features do radicals have?

A
  • very reactive
  • neutral species
  • have one or more unpaired e-
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43
Q

Define reaction mechanisms

A

Models that show the movement of electron pairs during a reaction

44
Q

Define radicals

A

Species with one or more unpaired e-

45
Q

Define homolytic fission

A

When each bonding atom receives one electron from the bonded pair

46
Q

Define heterolytic fission

A

When one bonding atom receives both electrons from the bonded pair

47
Q

Describe heteroltyic fission

A

When a covalent bond breaks and both electrons from the bond go to one of the bonded atoms. Results in a positive ion and a negative ion

48
Q

Why are carbocations reactive?

A

They are very reactive intermediates because they are unstable

49
Q

How is a covalent bond formed?

A

When 2 radicals or 2 oppositely charged ions collide they form a covalent bond

50
Q

Define homologous series

A

A family of organic compounds that have the same functional group but successive members differ by CH2

51
Q

Describe 4 features of alkanes

A
  • saturated (only single bonds)
  • have the general formula CnH2n+2
  • have a gradation in physical properties
  • similar chemical properties
52
Q

What are the bond angles around a C atom in alkanes?

A

109.5

53
Q

How do boiling points of alkanes increase?

A

They increase as the carbon chain length of the molecule increases because the surface area increases which increases the number of induced dipole dipole forces

54
Q

How does branching affect boiling point?

A

More branching lowers surface area which decreases the amount of intermolecular forces so also decreases the amount of energy needed to break the forces

55
Q

Why do alkanes have low reactivity with many reagents?

A
  • large amount of energy needed to break bonds (high bond enthalpies)
  • C-H sigma bonds have very low polarity
56
Q

What are alkanes often used as and why?

A

Fuels because they transfer chemical energy into usable form such as thermal

57
Q

What reaction is involved in combustion of alkanes?

A

A rapid oxidation reaction which combines oxygen with another substance

58
Q

Describe the process of complete combustion

A
  • in presence of plenty of air
  • makes clean blue flame and transfers max thermal energy because it fully oxidises carbon and hydrogen
  • only produces water and carbon dioxide
59
Q

Describe the process of incomplete combustion

A
  • limited supply of oxygen
  • produces carbon, water, carbon dioxide and carbon monoxide
  • makes a cooler dirty yellow flame
60
Q

How are halogenated organic compounds formed?

A

Alkanes react with chlorine and bromine in the presence of UV light

61
Q

Describe the halogenation process

A
  • homolytic fission of halogen forms radicals
  • H atom subbed for halogen atom
  • only continues if conditions are maintained
62
Q

Describe the 3 stages of the radical substitution mechanism

A
  1. initiation - formation of radicals
  2. propagation - 2 repeated steps that build up the desired product in a side reaction
  3. termination - 2 radicals collide and make a stable product
63
Q

Why is radical substitution unpredictable and hard to control?

A
  • reactions are randomly caused by a very reactive radical colliding with another species
  • mixture of products are formed and they must be separated so they can be used by fractional distillation or chromatography
64
Q

What are the conditions for chlorination of methane initiation too happen?

A

UV light or temp of around 300 degrees C

65
Q

Does chlorination of methane have a high or low atom economy?

A

Low - there are lots of products but only one is desirable

66
Q

State 5 features of alkenes

A
  • they’re hydrocarbons
  • they’re unsaturated, they contain at least one C=C bond
  • their general formula is CnH2n (only non cyclic)
  • they have a gradation in physical properties
  • they have similar chemical properties
67
Q

Describe the bonding in alkenes

A
  • C-H bonds are sigma bonds
  • C=C bonds are a sigmas bond and a pi bond (pi bond only ever formed after sigma bond and pi bond also breaks before sigma bond)
68
Q

Why is there restricted rotation in alkenes?

A
  • the pi bond restricts rotation around the double bond which makes alkenes planar in the region of the double bonds
69
Q

What bond angle is there around a double bond in an alkene?

A

120 degrees

70
Q

What are stereoisomers?

A

Compounds that have the same structural formula but different arrangements of atoms in space

71
Q

When can steroisomers be formed?

A

If an alkene has different alkyl groups attached to both carbons in double bond then stereoisomers can be formed

72
Q

Why can E/Z isomers be formed in compounds?

A

Because of the restricted rotation around the double carbon bond

73
Q

When can cis/trans isomers be formed in compounds?

A

When there is an H atom attached to both carbons in the double bond

74
Q

Are alkenes more or less reactive than alkanes?

A

More

75
Q

How does mean bond enthalpy relate to alkene reactivity?

A
  • the average energy required for one mole of a given bond to undergo homolytic fission in the gaseous state
76
Q

What special features does a double bond have in an alkene?

A
  • area of high electron density
  • attracts electrophiles like Br2, HBr and NO2+
77
Q

Define electrophile

A

An electron-pair acceptor. Examples include positive ions and molecules with a delta positive region of charge

78
Q

What is an addition reaction?

A

2 or more molecules bonded to make one product

79
Q

Describe how addition reactions occur in alkenes

A
  • pi bond breaks and small molecule is added across the 2 C atoms that were in the double bond
  • forms saturated organic product
80
Q

What is the general equation for addition reactions in alkenes?

A

C2H4 + X-Y –> C2H4XY

81
Q

What is hydrogenation and what condition must it occur in?

A
  • addition reaction in which hydrogen is added across a C=C bond
  • conditions: 150 degress celsius and catalyst
82
Q

What is an example of a catalyst that could be used in hydrogenation?

A

Nickel

83
Q

What is halogenation?

A
  • when halogen is added across a C=C bond
84
Q

Describe the products of halogenation

A
  • alkene becomes saturated
  • dihaloalkane is produced
85
Q

What can halogenation be used as a test for?

A

Saturation
- when a halogen is mixed with a saturated compound there is no reaction
- when they are mixed with an unsaturated compound, there is an addition reaction

86
Q

What occurs when an addition reaction with an alkene and a halogen happens?

A

Decolourisation

87
Q

In an electrophilic addition reaction, what occurs when starting the reaction?

A
  • Br2 is non-polar however C=C bond is rich e- area and induces dipole
  • delta positive side of the molecule is attracted to the double bond
88
Q

In an electrophilic addition reaction, what occurs during the reaction intermediates?

A
  • e- from pi bond make bond with Br atom causing heterolytic fission of Br molecule
  • positive charge remains on one C atom (forms carbocations which are very reactive)
89
Q

In an electrophilic addition reaction, what occurs during the formation of 1,2-dibromopropane?

A
  • 2 e- from the bromide ion are shared with the carbocation making a second bond and a more stable product
90
Q

What is hydration?

A
  • an addition reaction between a gaseous alkene and steam
  • used in industry to make alcohols
91
Q

What conditions are needed for hydration to occur?

A
  • high temp (300 degrees C)
  • high pressure (65atm)
  • phosphoric acid catalyst
92
Q

Describe the reaction of addition of hydrogen halides

A
  • addition reaction in which a hydrogen halide is added across the C=C bond
  • produces haloalkanes
  • at least one H atom is replaced by a halogen atom
  • hydrogen halides are gas at RTP so they are bubbled through the alkene to cause a reaction
93
Q

What is Markownikoff’s rule?

A

‘In electrophilic addition to alkenes the major product is formed via the more stable carbocation’
eg. If there is a product with a tertiary carbocation and one with a primary carbocation, the tertiary one will be the major product

94
Q

What is the order of stability in carbocations?

A

methyl is less stable than primary which is less stable than secondary which is less stable than tertiary

95
Q

How would you write the name of a polymer of chloroethene?

A

Poly(chloroethene)

96
Q

Define biodegradable

A

Affected by the action of microorganisms and environmental conditions, leading to decomposition

97
Q

Define bioplastic

A

Material made from a renewable source that is biodegradable

98
Q

How are biodegradable polymers created?

A

Sometimes biodegradable polymers (like plant starch) are mixed with an addition polymer (like poly(ethene))
- over time the plant starch breaks down and smaller polymer chains are made
- this leads to biodegrading

99
Q

What is the concern about biodegradable polymers even though they break down into smaller polymer chains?

A

They smaller polymer chains can still do damage to the environment

100
Q

When can a material be classified as a bioplastic?

A

When only the biodegradable polymer is used

101
Q

What can plant starch be used to make?

A

Bin bags

102
Q

When can a material be classified as carbon neutral?

A

If the material used to make them is derived from sustainable farming, the material can be classified as carbon neutral

103
Q

What conditions must a material fall under for it to be classified as fully compostable?

A
  • plastic must decompose as quickly as grass to compost
  • only products should be water, carbon dioxide, inorganic ions and biomass
104
Q

Describe poly(lactic acid)

A
  • decomposes in around 180 days
  • used to make cold drink cups and to wrap fruits and vegetables
105
Q

How do photodegradable polymers break down?

A
  • break down chemically using energy with wavelengths similar to light
  • they are either addition polymers with bonds within their structure that are weakened by absorption of light OR they have an additive that’s affected by light
106
Q

Is the break down of photodegradable polymers possible to stop?

A

No, once the polymer has been exposed to light, it begins to break down and the process is impossible to stop

107
Q

What is the issue with photodegradable polymers in landfill?

A

They may not be exposed to sufficient light for them to degrade

Chemistry (17 decks)

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